Sperm adhesion in sea urchins is mediated by bindin, a protein located in the acrosomal granule at the apex of the sperm head. The long term objectives of my research program are to understand the detailed structure, organization and function of fertilization of bindin. I propose to investigate the molecular basis of adhesive specificity and the underlying mechanisms of adhesive force generation. My working hypothesis is that bindin specifically interacts with a fucose-containing glycoconjugate on the egg surface. I propose experiments that will further characterize the structure of the egg surface glycoconjugate and the polysaccharide binding domain of the bindin polypeptide as well as the molecular nature of their specific interaction. These experiments should provide a significant advancement of our understanding of the general problem of the molecular basis of cellular recognition and adhesion. I also propose to investigate the formation of membrane-like vesicles by bindin and the possible significance of this phenomenon to the biochemistry of plasma membrane proteins in general and sperm-egg plasma membrane fusion in particular. Preliminary observations suggest that a conformation change occurs in the bindin polypeptide resulting in the formation of protein-rich vesicles which resemble lipid bilayers in the electron microscope. In contrast to lipid vesicles, these bindin vesicles are stable in non-ionic detergents, but are disrupted by proteolysis or other treatments which solubilize proteins. I propose to further characterize this apparent conformation change as well as the processes which regulate this transformation. In addition, I hope to exploit this membrane-like vesicle forming property of bindin to determine the structure and organization of the bindin polypeptide in these vesicles at a high level of resolution. Knowledge gained through these investigations may ultimately be useful for our understanding of the causes of infertility in man and domestic animals as well as the development of nonhormonal methods of contraception based on the inhibition of gamete interaction.